Steering Wheel Shimmy

A year ago, I replaced a bent wheel on my 2010 Mustang because it was causing violent shaking in steering wheel while driving down road at certain speeds. After replacing wheel, things go much smoother. Lately, when I apply my brakes at around 40-45 mph steering wheel starts shaking, when it gets below to about 20-25, shaking goes away. Does this sound like the rotor or what could it be? Oh and this morning when pulling out of garage, when I lightly applied brakes, I could hear a squealing.
Please help with your suggestions and diagnosis.

Both the shimmy and squeal could be warped rotors.
I got my car in 12/06 and within a few months the brakes squealed.
Just like yours, moving very slowly with light braking.
The dealer machined the rotors. Problem fixed, for a while.
A year later I coated the pads with disc brake quiet.That worked for a few years.
The squeal came back and i started noticing a braking shimmy as well.
I replaced the rotors and front pads. I coated the new pads with disc
brake quiet and let them dry overnight.
In my case the new rotors fixed the braking shimmy and possibly the squeal as well.
My factory pads were in great shape. Did I need new pads? Maybe not, but i was sick of that squeal so I did the pads when i did the rotors.

Edit: Did you hit something to bend the wheel or just a defective wheel?

If it doesn't begin shaking until you apply the brakes then I'd say rotors. The squeling you heard when first applying the brakes while sitting overnite was likely just some light corrosion due to water or simply a humid night, providing it stopped after the 2nd or 3rd application of the brakes. Nothing to worry about if that's all it was.

I didn't hit anything to cause a bent wheel, but it was a lease car on a dealership lot. I got them to deal with me and replace the wheel after I had discovered it much later on. I think the leasee caused the problem and it probably messed up the rotor on that wheel. Do you have to buy rotors by the pair or can you buy just the one?

To answer your question, replace the rotors in pairs and consider new pads while you are at it. It's all relative, but rotors are not that expensive and the pads are even less so. It's a job most people can do themselves in a few hours if you're the least bit mechanically inclined.

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